Trucks and tractors are often referred to as 4×2, 6×4, 6×6, 8×8, 10×8, or 10×10 configurations based on the number of wheels and the number of driven wheels. A 6×4 configuration, for example, has three axles of at least two wheels each. Two of the axles (at least 4 wheels) are driven axles. Generally, each rear driven axle comprises a pair of half-shafts, each half-shaft on an opposite side of an axle assembly. Thus a truck with a 6×4 configuration would have at least four half-shafts being driven.
FIG. 1 shows an example of a 6×4 truck 1. The truck 1 includes three axles supporting the wheels (a set of front wheels on a front axle 10, a set of intermediate wheels on an intermediate axle 20, and a set of rear wheels on a rear axle 30). In the truck 1 shown, it should be understood that the intermediate wheels/axle 20 and the rearmost wheels/axle 30 are both driven axles.
FIG. 2 shows a schematic of the underside of the conventional 6×4 truck 1 from FIG. 1. The truck includes an engine 2, transmission 3, drive shaft 4, an intermediate axle assembly 5 and a rear axle assembly 6. Each axle assembly can include a differential. Each axle assembly 5, 6 is capable of transmitting motion from the drive shaft 4 to a pair of half-shafts 7. As seen in FIG. 2, the half-shafts 7 attached to the intermediate axle assembly 5 are shown in their normal operating position, while the half-shafts 7 associated with the rear axle assembly 6 have been “pulled” or removed from rotational engagement with the rear axle assembly 6, generally by moving each half-shaft 7 outward along its rotational axis.
Most current commercial trucks and tractors are heavy, and require special equipment when towed. These trucks may be towed after becoming disabled, or simply towed from the assembly plant to the dealership. Towing new trucks to dealerships avoids unnecessary mileage on the trucks. Trucks being delivered may be piggy-backed with one another to allow a single driver to transport a plurality of trucks. During towing, the cabin end of the truck or trailer is generally lifted off the ground by the towing truck, while one or more rear axles of the truck remain in contact with the road. Conventionally trucks are preferably towed only after the half-shafts 7 are “pulled.” This labor intensive process can involve manually removing or “pulling” the half-shafts 7 from engagement with each axle assembly 5, 6. With the half-shafts pulled, the respective wheels are free to rotate without moving parts within each axle assembly 5, 6.
In situations where the half-shafts 7 are not pulled, wheel rotation will cause rotation of moving parts within the axle assemblies, particularly differentials therein. Rotation can also be transferred up to the transmission 3. In this case, extensive and expensive damage can occur within the transmission 3 or the differentials due to burn out, caused by insufficient lubrication within the transmission, and insufficient speed compensation within the differentials. If a 6×4 truck is being towed with both driven axles contacting the road (and half-shafts in place), the rotation of the wheels is passed to the half-shafts 7, through to an intermediate drive axle 8, forward through the drive axle 4 and into the transmission box 3. The transmission 3 may be in neutral, allowing the movement of the gears inside; however, available lubrication may be insufficient. During towing, the transmission 3 is likely tilted at an angle, causing a shift in the lubricating oil and preventing some gears or other components from being properly submerged and lubricated by oil splash. While driving, transmission gears may also be lubricated with active lubrication. In active lubrication, transmission fluid is sprayed, by a pump, onto the moving transmission parts, at a specified angle, to keep them moving freely. This spraying only occurs when the engine 2 is running and the transmission 3 is engaged through a mechanical clutch. The splashing of the submerged rotating gears can provide some lubrication but, by itself, the splashing is not likely sufficient to lubricate bearings and other components assembled in critical corners of the transmission. Therefore, while the truck is being towed with half-shafts 7 in place, the transmission parts are rotating with respect to one another without being properly lubricated. The moving parts can quickly become hot, burn, fall-apart or even fuse together.
If a 6×4 truck is being towed with the half-shafts engaged and only the rearmost wheels contacting the road, rotation of the rearmost wheels transmits motion to an interaxle differential within the intermediate axle assembly 5. The interaxle differential allows the rearmost wheels to rotate at a different speed than the intermediate wheels. Differentials are designed, however, to compensate for short term, relatively slight differences in speed. When the intermediate wheels are raised from surface contact (by the towing truck), the intermediate wheels will not be spinning as the truck is towed. This extreme speed difference between the intermediate wheels and the rearmost wheels can overwork the differential, potentially burning out the components therein and again causing the need for significant repairs.
Although pulling the half-shafts would alleviate this problem, in practice, this labor intensive process is often impractical or avoided. In the case of a disabled truck, environmental conditions may simply not allow the time and space necessary to perform this mechanical adaptation. For example, a disabled tractor along the highway may be surrounded by minimal, if any, shoulder. Further, highway authorities often require removal of a disabled truck as soon as possible, to allow other traffic to resume normal flow, even if that means leaving the half shafts in place. Prior to delivery, the need to disassemble or “pull” half-shafts provides an additional opportunity for error when the axles are reassembled upon delivery. For example, improper re-assembly of half-shafts can cause wheel end lubrication oil leaks.
Given the potential damage to moving parts, it has been suggested that the drive shaft 4 may be dropped, instead of pulling the rear half-shafts 7. This process involves manually removing the connection between the drive shaft 4 and the rear axles. However, this process is also labor and space intensive.
Accordingly, there is a need for a drive train configuration that allows for towing a rear axle driven truck that limits or eliminates damage to moving parts and avoids the manual, labor-intensive solutions of pulling the half-shafts or dropping the drive shaft when one or more driven rear axles remain in contact with the road.
Some embodiments of the present disclosure include a vehicle having at least one rear driven axle. The vehicle includes a transmission, a main drive shaft, and a rear axle assembly. The rear axle assembly can selectively transmit power from the transmission to a rearmost set of wheels of the vehicle. To selectively transmit power, the rear axle assembly can include a rear axle input shaft, a neutralizer, a differential input shaft, and a differential. The neutralizer is used to mechanically connect and disconnect the rear axle input shaft from the differential input shaft.